Air compressors are commonly used to supply compressed air for air separation plants and other types of plants. Frequently the plant capacity is larger than that of the air compressor initially installed. Often, at some time after the initial installation, an increase in the plant production rate is desired necessitating increased air compressor capacity.
Methods used in the past to increase the air compressor capacity have been to replace the existing compressor with a new larger compressor, to install a complementary compressor in parallel with the existing compressor, or to retrofit the existing compressor with internal parts having higher flow capacity. Plant air compressors are often multistage units with intercooling and aftercooling. Sizes range from 500 HP to 15,000 HP.
Thus replacement of an existing compressor with a new compressor of higher capacity usually cannot be economically justified because of the high capital cost. Retrofit of an existing machine involves replacement of the major rotating assemblies which are typically 25 to 30% of the initial cost of the unit, and is also usually economically unattractive. The installation of a complementary compressor in parallel with an existing compressor has been most often practiced as the most economical and thus most attractive alternative. This invention provides a more attractive and advantageous alternative to the prior art methods mentioned.
Accordingly an object of this invention is to provide a method and apparatus for increasing the capacity of an existing compressor.
Features of this invention are that the apparatus involves little added mechanical complexity and lower capital cost than prior methods.
Advantages of this invention are a savings in operating power in the compressor operation and some capability of adjusting the compressor capacity without a performance penalty.